Dimension-six top-quark Higgs-boson interaction and its effect in collider phenomenology

Measurement of the Yukawa interaction between the top quark and the Higgs boson should be useful to clarify the mechanism of fermion mass generation. We discuss the impact of nonstandard interactions characterized by dimension-six operators on the effective top Yukawa coupling. The cross section of the process e-e+→W-W+νν̄→tt̄νν̄ is calculated including these operators, and possible deviation from the standard model prediction is evaluated under the constraint from perturbative unitarity and current experimental data. We find that if the new physics scale is in a TeV region, the cross section can be significantly enhanced due to the nonstandard interactions. Such a large effect should be detectable at the International Linear Collider.